1. Field of the Invention
The present invention relates to a solid electrolytic capacitor for mounting on a printed wiring board and a method of making the same.
2. Description of the Related Art
FIGS. 34 and 35 illustrate an example of prior art tantalum solid electrolytic capacitor (hereinafter simply referred to as xe2x80x9csolid electrolytic capacitorxe2x80x9d). The solid electrolytic capacitor 61 includes a cathode lead 62, an anode lead 63, a capacitor element C1 and a resin package 65 for partially sealing these elements. The capacitor element C1 includes an element body 64 and an anode wire 66 extending from an end surface 64a of the element body. The element body 64 is formed with a metal layer 67 for covering the outer surfaces thereof. The metal layer 67 is electrically connected to the cathode lead 62. The anode wire 66 is electrically connected to the anode lead 63. A method for making the solid electrolytic capacitor 61 will be described. First, an element body 64 is connected, with a conductive adhesive 68, to a cathode lead 62 formed on a manufacture lead frame (not shown). Further, an anode wire 66 extending from the element body 64 is connected, by e.g. spot welding, to an anode lead 63 similarly formed on the manufacture lead frame. Thereafter, these parts are sealed by a resin package 65 formed of an epoxy resin for example. Subsequently, the leads 62, 63 extending outward from the resin package 65 are separated from the manufacture lead frame. Then, each lead 62, 63 is bent to have a desired configuration.
In bending each lead 62, 63 into a desired configuration, a considerable bending stress is exerted on the resin package 65. Therefore, the solid electrolytic capacitor 61 need be strong enough to withstand the bending stress. Generally, damages due to the bending stress are prevented by making the resin package 65 relatively thick. However, an increase in the thickness of the resin package 65 provides a large thickness at a portion other than the element body 64, which leads to an increase in the product size.
Recently, there is an increasing need for a solid electrolytic capacitor 61 of a high capacitance. Generally, to provide a solid electrolytic capacitor of a high capacitance, the size of the capacitor element itself need be increased. For this purpose, the size of the solid electrolytic capacitor accommodating the element need be increased.
However, the mounting density of a printed wiring board for mounting a solid electrolytic capacitor 61 becomes higher in accordance with the size reduction of electronic components. Therefore, a solid electrolytic capacitor 61 also need be reduced in size. Thus, it is not desirable to increase the size of the solid electrolytic capacitor to provide a higher capacitance.
Further, in the capacitor element C1, the anode wire 66 extending from the element body 64 is made of tantalum for example. Therefore, good conduction cannot be established between the anode wire 66 and the anode Lead 63 made of e.g. copper because of the affinity between the materials.
It is, therefore, an object of the present invention to provide a solid electrolytic capacitor which is capable eliminating or at least reducing the problems described above.
According to a first aspect of the present invention, there is provided a solid electrolytic capacitor comprising a capacitor element including an element body and a conductive wire extending therefrom, a first electrode electrically connected to the element body, a second electrode electrically connected to the conductive wire, and a resin package integrally sealing said parts. Each of the first electrode and the second electrode comprises a conductive plate and has a lower surface exposed at a lower surface of the resin package for serving as a terminal surface. The first electrode has an upper surface to which the element body is connected, and the second electrode has an upper surface to which the conductive wire is connected via a conductive bolster.
Preferably, the lower surface of the first electrode is stepped, and the upper surface is larger in area than the terminal surface.
Preferably, the lower surface of the first electrode is partially etched to be stepped.
Preferably, the upper surface of the second electrode has an edge formed with a stepped portion.
Preferably, the stepped portion is formed by partially etching the upper surface of the second electrode.
Preferably, the conductive bolster is in the form of a rectangular parallelepiped, and at least one end surface of the conductive bolster is exposed at a side surface of the resin package.
Preferably, the conductive wire is formed of tantalum, whereas the conductive bolster is formed of nickel or an alloy containing nickel. The two members are connected to each other by resistance welding.
Preferably, the element body is connected to the upper surface of the first electrode with a conductive adhesive, and the conductive bolster is connected to the upper surface of the second electrode with a conductive adhesive.
According to a second aspect of the present invention, there is provided a method of making a solid electrolytic capacitor which comprises a capacitor element including an element body and a conductive wire extending therefrom, and a resin package for sealing the capacitor element. The method comprises preparing a plate-like fabrication frame including a plurality of unit regions arranged in a matrix. Each of the unit regions includes a first electrode and a second electrode having respective inner ends spaced from each other by a predetermined distance. An element body of a capacitor element is connected to an upper surface of each of the first electrodes, whereas a conductive wire extending from the element body is connected to an upper surface of a corresponding one of the second electrodes via a conductive bolster. An intermediate article is provided by resin-sealing the fabrication frame to enclose the capacitor elements while exposing the lower surfaces of the first electrodes and the second electrodes. The intermediate article is divided into each of the unit regions.
Preferably, the conductive bolster is connected to the conductive wire by resistance welding. The element body is connected to the upper surface of the first electrode with a conductive adhesive, whereas the conductive bolster is connected to the upper surface of the second electrode with a conductive adhesive.
According to a third aspect of the present invention, there is provided a solid electrolytic capacitor comprising a substrate having an upper surface formed with a first and a second electrodes and a lower surface formed with terminal surfaces electrically connected to the first and the second electrodes, respectively, a capacitor element including an element body and a conductive wire extending therefrom, and a resin package for sealing the capacitor element. The element body is connected to the first electrode of the substrate, and the conductive wire is connected to the second electrode of the substrate via a conductive bolster.
Preferably, the conductive bolster is in the form of a rectangular parallelepiped, and at least one end surface of the conductive bolster is exposed at a side surface of the resin package.
Preferably, the conductive wire is formed of tantalum, and the conductive bolster is formed of nickel or an alloy containing nickel. The two members may be connected to each other by resistance welding.
Preferably, the element body is connected to the upper surface of the first electrode with a conductive adhesive, whereas the conductive bolster is connected to the upper surface of the second electrode with a conductive adhesive.
According to a fourth aspect of the present invention, there is provided a method of making a solid electrolytic capacitor which comprises a capacitor element including an element body and a conductive wire extending therefrom, and a resin package for sealing the capacitor element. The method comprises preparing a material board including a plurality of unit regions arranged in a matrix. Each of the unit regions includes an upper surface formed with a first and a second electrodes having respective inner ends spaced from each other by a predetermined distance, and a reverse surface formed with terminal surfaces electrically connected to the first and the second electrodes, respectively. An element body of a capacitor element is connected to each of the first electrodes. A conductive wire extending from the element body is connected to a corresponding one of the second electrodes via a conductive bolster. An intermediate article is provided by resin-sealing the material board to enclose the capacitor elements while exposing the terminal surfaces. The intermediate article is divided into each of the unit regions.
Preferably, the conductive bolster is connected to the second electrode by resistance welding. The element body is connected to the first electrode with a conductive adhesive, whereas the conductive bolster is connected to the second electrode with a conductive adhesive.
Other features and advantages of the present invention will become clearer from the description of the preferred embodiment given below with reference to the accompanying drawings.